Polyolefin resins typified by polypropylene are used for diverse applications since they are inexpensive, excellent in moldability and also excellent in the balance of physical properties such as stiffness. For application as molded resin articles, the resins are used as automobile members and containers owing to the mechanical properties of the resins. For application as films, the resins are used as packaging films for foods such as confectionery owing to the moisture resistance and moisture-proof property thereof. Further, for application as fibers, nonwoven fabrics formed of the resins are popularly used as sanitary materials such as disposable diapers.
However, since petroleum-derived materials have such problems as the depletion of oil resource, the generation of carbon dioxide at the times of production and incineration disposal, and non-degradability as waste. So, in recent years, biodegradable resins and organism-derived materials attract attention.
Among biodegradable resins, especially polylactic acid resins mainly composed of lactic acid monomer are expected as biopolymers that can substitute the resins produced from fossil raw materials such as petroleum for such reasons that lactic acid monomer can be produced at low cost with the biomass of corns or the like as a raw material by fermentation methods using microbes and that the melting point is as high as about 170° C. to allow melt molding.
However, polylactic acid resins are unsuitable for use as molded articles via crystallization, since they are low in crystallization rate. For example, in the case where polylactic acid resins are injection-molded, there are such large problems concerned with moldability and heat resistance to be addressed for practical application that the molding cycle time is too long, that heat treatment is necessary after molding, and that deformation at the times of molding, and heat treatment is large.
On the other hand, techniques of mixing multiple resins are widely known as polymer alloy techniques and are widely used for the purpose of improving the disadvantages of individual polymers.
JP 05-179110 A discloses a microbially degradable thermoplastic resin composition, in which polyolefin resins are mixed and dispersed in a microbially decomposable thermoplastic resin, one of the polyolefin resins being a modified polyolefin resin. However, JP 05-179110 A is intended to control the microbial degradability, and does not suggest at all any solving means for obtaining a resin composition excellent in all the properties of moldability, impact resistance, heat resistance and the like.
JP 06-263892 A discloses a microbially degradable thermoplastic resin film formed of a composition, in which a compatibilizing agent is mixed with a mixture consisting of an aliphatic polyester and a polyolefin resin. However, though the film of JP 06-263892 A has high microbial degradability and thermal fusion bondability since the sea component is an aliphatic polyester, the patent document does not suggest at all any solving means for obtaining a resin composition excellent in all the properties of moldability, impact resistance, heat resistance and the like.
JP 2003-301077 A discloses a polyolefin resin composition containing a polyolefin resin, polylactic acid-based synthetic resin component, vinyl acetate/ethylene copolymer and the like. However, JP 2003-301077 A is intended for stable productivity in the processing for forming a sheet-like material, and does not disclose anything about heat-resistance at all. The document does not suggest at all any solving means for obtaining a resin composition excellent in all the properties of moldability, impact resistance, heat resistance and the like.
JP 2005-68232 A discloses a biodegradable blend resin obtained by blending a biodegradable resin and a polyolefin resin. However JP 2005-68232 A is intended to obtain a laminate film with a high interlayer adhesive strength, and does not suggest at all any solving means for obtaining a resin composition excellent in all the properties of moldability, impact resistance, heat resistance and the like.
JP 2005-248160 A discloses a biodegradable plastic material obtained by mixing a biodegradable polymer, a polymer other than a biodegradable polymer and a compatibilizing agent. However, JP 2005-248160 A is insufficient in the effect of enhancing heat resistance, and does not suggest at all any solving means for obtaining a resin composition excellent in all the properties of moldability, impact resistance, heat resistance and the like.
JP 2005-307128 A discloses a polylactic acid resin composition containing a polylactic acid resin, modified polypropylene resin and inorganic filler. However, though JP 2005-307128 A has an effect of enhancing heat resistance to some extent, the disclosure is not sufficient yet and does not suggest at all any solving means for obtaining a resin composition excellent in all the properties of moldability, impact resistance, heat resistance and the like.
As described above, even if any of the above-mentioned methods is used, it is very difficult to obtain a resin composition satisfying all the properties of moldability, impact resistance, heat resistance and the like. There are many demands for materials that can be used without any practical problem, and it is desired to further improve the presently available materials.
It could therefore be helpful to provide a molded article that contains a biodegradable resin low in environmental load such as polylactic acid, has productivity equivalent to that of presently available molded polyolefin articles and also has moisture-proof property, dimensional stability and the like equivalent to those of presently available articles.